As a sealant for solid oxide fuel cells (SOFC), a mixture powder has been used consisting of an amorphous glass powder and a ceramic powder which has a high coefficient of thermal expansion (see Patent Document 1). With this sealant, however, there has been a problem that its application is limited only to such structural parts that are stably supported already and do not require a sealant to sustain any load (including its own weight), for at the operation temperatures of solid oxide fuel cells, which is very high like 700-1000° C., there occurs reduction of high-temperature viscosity of the amorphous glass, rendering the sealant more likely to undergo deformation and even hardly capable of sustaining itself.
Further, there have also been proposed a crystallized glass in which lithium disilicate is primarily precipitated or a SiO2—Al2O3—ZnO—K2O—Na2O-based amorphous glass (see Patent Documents 2 and 3, respectively). However, these sealants contain a large amount of alkali metals either in the crystalline phase precipitated from the starting glass or in the remaining glass phase. Therefore, they have problems in respect to durability of their insulation property and sealing integrity, and are expected, after prolonged use of the SOFC, to become more likely to end in failure of insulation or breakage of the seal, under the influence of high-temperature and humid conditions in which it operates.    [Patent Document 1] Japanese Patent Application Publication H8-134434    [Patent Document 2] Japanese Patent Application Publication 2003-238201    [Patent Document 3] Japanese Patent Application Publication 2004-123496